Method for establishing apparent formation water resistivity chart by considering lithologic change

Abstract

A method for establishing an apparent formation water resistivity chart by considering lithology change belongs to the technical field of reservoir fluid identification, and comprises the following steps: extracting a density and interval transit time curve reflecting reservoir physical properties, a natural gamma curve reflecting lithology and a deep induced resistivity curve reflecting reservoir electrical properties, and calculating through a formula to obtain a resistivity chart of apparent formation water; and obtaining the apparent formation water resistivity and a natural gamma relative value, and establishing an apparent formation water resistivity chart. For an argillaceous sandstone oil and gas reservoir, the resistivity value of the argillaceous sandstone oil and gas reservoir is reduced along with thinning of lithology and increase of the argillaceous content, while a water layer is often coarse in lithology, low in argillaceous component and not low in resistivity, and certain difficulty is brought to fluid identification of the reservoir; according to the method for establishing the apparent formation water resistivity chart by considering the lithologic change, the lithologic factors of low-resistance formation causes are considered, the relative value chart of the apparent formation water resistivity and the natural gamma is established, and a low-resistance oil-water layer caused by large reservoir lithologic and physical property changes can be well identified.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of reservoir fluid identification, and particularly relates to a method for establishing a formation water resistivity chart considering lithology change. BACKGROUND

[0002] For fresh water drilling fluid, among a plurality of effectively fused parameters of logging information, the apparent formation water resistivity Rwa is a comprehensive parameter effectively fused by resistivity and porosity information under a certain assumption premise, which reflects the oil-bearing information of the reservoir. However, for the identification of low-resistance oil-water layers, the resistances of oil and gas layers and water layers appear to be crossed due to different lithologies, which brings certain difficulty to fluid identification. For example, the resistivity value of a muddy sandstone oil and gas layer decreases with the increase of lithology and the content of mud, while the resistivity of a water layer is not low due to the coarse lithology and low mud content. In the case of similar properties, the apparent formation water resistivities Rwa of low-resistance oil and gas layers and water layers appear to be crossed. Fortunately, the low-resistance oil and gas layers and water layers are different in lithology, and when the apparent formation water resistivities Rwa of the low-resistance oil and gas layers and water layers are similar, the lithology factor of low-resistance origin can be considered to distinguish them. Therefore, the establishment of the apparent formation water resistivity chart considering the lithology factor is of great significance to the identification of low-resistance oil-water layers. SUMMARY

[0003] In order to solve the above problems, the application provides a method for establishing an apparent formation water resistivity chart considering lithology change, extracts density and acoustic travel time curves reflecting reservoir properties, natural gamma curves reflecting lithology and deep induction resistivity curves reflecting reservoir electrical properties, obtains apparent formation water resistivity and natural gamma relative value through formula calculation, and establishes an apparent formation water resistivity chart.

[0004] Further, the method comprises the following steps:

[0005] S1, for the logging curves of the study area, a standard layer is selected, the logging curves are standardized, and the calculation density, acoustic travel time, natural gamma and deep induction resistivity geological parameters are ensured to reach a unified precision.

[0006] Further, the method further comprises the following steps: S2, reading the deep induction resistivity and acoustic travel time, density logging characteristic values of the target layer section, and calculating the apparent formation water resistivity by using a formula.

[0007] Further, the method further comprises the following steps: S3, reading the natural gamma value, the maximum value of natural gamma and the minimum value of natural gamma of the target layer section, and calculating the natural gamma relative value by using a formula.

[0008] Further, the method further comprises the following step: S4, establishing a crossplot of apparent formation water resistivity and relative value of natural gamma according to the calculation result, i.e. apparent formation water resistivity chart.

[0009] Further, in the step S1, the logging curves are first standardized, mainly by using regional standard layers to adopt histogram standardization.

[0010] Further, in the step S2, the deep induction resistivity and the acoustic travel time and density logging characteristic values of the target layer section are read, and the apparent formation water resistivity is calculated by using a formula;

[0011] The calculation formula of the apparent formation water resistivity is as follows:

[0012]

[0013] R wa =R t / F

[0014] R wa =R t ＊ Φ m / a

[0015] In the formula:

[0016] F – formation factor;

[0017] Rwa – apparent formation water resistivity;

[0018] Rt – deep induction resistivity;

[0019] m – rock cementation index;

[0020] a – lithology coefficient related to lithology;

[0021] φ – porosity;

[0022] Ro is the resistivity of the rock when it is completely water-containing;

[0023] Rw is the formation water resistivity.

[0024] Further, in the step S3, the natural gamma value, the maximum value of natural gamma and the minimum value of natural gamma of the target layer section are read, and the relative value of natural gamma is calculated by using a formula;

[0025] The calculation formula of the relative value of natural gamma is as follows:

[0026]

[0027] In the formula: GR – natural gamma value;

[0028] △GR – relative value of natural gamma;

[0029] GRmin - natural gamma minimum value;

[0030] GRmax - natural gamma maximum value.

[0031] The beneficial effect of the present application is that the present application is a method for establishing a pseudo formation water resistivity chart considering lithology change, for argillaceous sandstone oil and gas layers, the resistivity value decreases with the decrease of lithology and the increase of argillaceous content, while the water layer is often coarse in lithology and low in argillaceous content, and the resistivity is often not low, which brings certain difficulty to the fluid identification of the reservoir, the present application considers the lithology factor of low resistance cause, establishes a pseudo formation water resistivity and natural gamma relative value chart, and can well identify the low resistance oil and water layer caused by large changes in reservoir lithology and physical property.

[0032] The present application provides a method for establishing a pseudo formation water resistivity chart considering lithology change, to realize the identification of the low resistance oil and water layer caused by large changes in reservoir lithology and physical property, which extracts the density and acoustic travel time curve reflecting the physical property of the reservoir, the natural gamma curve reflecting the lithology, and the deep induction resistivity curve reflecting the electrical property of the reservoir, obtains the pseudo formation water resistivity and the natural gamma relative value through formula calculation, and establishes a pseudo formation water resistivity chart, the present application is simple in operation and low in cost. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is the main operation process flowchart of the present application;

[0034] Figure 2 is a pseudo formation water resistivity chart. DETAILED DESCRIPTION

[0035] In order to make the technical means adopted by the present application and the purpose easy to understand, the present application is further described below in combination with specific embodiments, a method for establishing a pseudo formation water resistivity chart considering lithology change, comprising the following steps:

[0036] S1, for the logging curves of the study area, selecting a standard layer, normalizing the logging curves, and ensuring that the geological parameters such as calculated density, acoustic travel time, natural gamma and deep induction resistivity reach a unified precision;

[0037] S2, reading the deep induction resistivity and acoustic travel time, density logging characteristic values of the target layer section, and calculating the pseudo formation water resistivity by using the formula;

[0038] S3, reading the natural gamma value, natural gamma maximum value and natural gamma minimum value of the target layer section, and calculating the natural gamma relative value by using the formula;

[0039] S4, according to the calculation result, establishing the cross plot of the pseudo formation water resistivity and the natural gamma relative value, that is, the pseudo formation water resistivity chart.

[0040] As Figure 1 shown, a method for establishing apparent formation water resistivity chart considering lithology change extracts density and acoustic travel time curves reflecting reservoir properties, natural gamma curve reflecting lithology and deep induced resistivity curve reflecting reservoir electrical property, and obtains apparent formation water resistivity and natural gamma relative value through formula calculation to establish apparent formation water resistivity chart.

[0041] 1) For the logging curves in the study area, standard layers are selected, and the logging curves are standardized to ensure that the geological parameters such as calculated density, acoustic travel time, natural gamma and deep induced resistivity reach a unified precision;

[0042] 2) Read the deep induced resistivity and acoustic travel time, density logging characteristic values of the target layer section; calculate the apparent formation water resistivity by using the formula;

[0043] The calculation formula of apparent formation water resistivity is as follows:

[0044]

[0045] R wa = R t / F

[0046] R wa = R t ＊ Φ m / a

[0047] In the formula:

[0048] F - formation factor;

[0049] Rwa - apparent formation water resistivity;

[0050] Rt - deep induced resistivity;

[0051] m - rock cementation index;

[0052] a - lithology coefficient related to lithology;

[0053] φ - porosity;

[0054] Ro is the resistivity of rock when it is completely water-containing;

[0055] Rw is the formation water resistivity.

[0056] 3) Read the natural gamma value, natural gamma maximum value and natural gamma minimum value of the target layer section; calculate the natural gamma relative value by using the formula;

[0057] The calculation formula of natural gamma relative value is as follows:

[0058]

[0059] GR - natural gamma value;

[0060] △GR - natural gamma relative value;

[0061] GRmin - natural gamma minimum value;

[0062] GRmax - natural gamma maximum value.

[0063] 4) According to the calculation results, a crossplot of apparent formation water resistivity and natural gamma relative value, i.e. apparent formation water resistivity chart is established.

[0064] As shown in Figure 2 , the chart uses 44 oil testing points and 3 outliers, and the chart coincidence rate is 93.2%.

[0065] The apparent formation water resistivity chart established by the calculation results is used to identify the fluid of the coring well and the key exploration well in the study area, and the identification results are consistent with the oil testing results. Among them, in a layer of a well, the natural potential appears negative anomaly, the acoustic time difference value is 240 μs / m, the density value is 2.3 g / cm 3 , the deep induction resistivity value is 28 Ω.m, according to the porosity calculation model Φ = -30.057 × DEN + 83.787, the porosity is 14.5%, combined with the core analysis, the rock-electricity parameter experimental data a = 1.0801, m = 1.8595 are obtained; the calculated apparent formation water resistivity is 0.71, the natural gamma value is 84 API, the maximum value is 88 API, the minimum value is 77 API, the calculated natural gamma relative value is 0.82, and the method is judged as oil-water layer. The layer was tested on January 6, 2007, with daily oil production of 4.68 t and daily water production of 3.6 m 3 , the oil testing conclusion is consistent with the identification result of the method, and the practicability of the method is verified.

[0066] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can make equivalent replacement or change according to the technical solution and concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method of establishing a pseudo-formation water resistivity chart taking into account lithology variations, characterized in that, The density and acoustic travel time curves of the extracted reaction reservoir properties, the natural gamma ray curve of the reaction lithology and the deep induced resistivity curve of the reaction reservoir electrical property are extracted, and the apparent formation water resistivity and the natural gamma ray relative value are obtained by formula calculation, and the apparent formation water resistivity chart is established.

2. The method for establishing a lithology-dependent water resistivity chart of claim 1, wherein, The method comprises the following steps: S1, for the logging curves of the research area, selecting the standard layer, normalizing the logging curves, and ensuring that the calculated density, acoustic travel time, natural gamma ray and deep induced resistivity geological parameters reach a unified precision.

3. The method for establishing a lithology-dependent water resistivity chart of claim 2, wherein, Further comprising the following steps: S2, reading the deep induced resistivity and acoustic travel time, density logging characteristic values of the target layer section, and calculating the apparent formation water resistivity by using the formula.

4. The method for establishing a lithology-dependent water resistivity chart of claim 3, wherein, Further comprising the following steps: S3, reading the natural gamma ray value, the maximum value and the minimum value of the natural gamma ray of the target layer section, and calculating the natural gamma ray relative value by using the formula.

5. The method for establishing a lithology-dependent water resistivity chart of claim 4, wherein, Further comprising the following steps: S4, according to the calculation results, establishing the cross plot of the apparent formation water resistivity and the natural gamma ray relative value, that is, the apparent formation water resistivity chart.

6. The method for establishing a lithology-dependent water resistivity chart of claim 2, wherein, In the step S1, the logging curves are first normalized, and the histogram normalization is used for the regional standard layer.

7. The method for establishing a lithology-dependent water resistivity chart of claim 3, wherein, In the step S2, the deep induced resistivity and acoustic travel time, density logging characteristic values of the target layer section are read, and the apparent formation water resistivity is calculated by using the formula; The calculation formula of the apparent formation water resistivity is as follows: In the formula: F is the formation factor; m is the rock cementation index; a is the lithology coefficient related to lithology; φ is the porosity; Ro is the resistivity of the rock when it is completely water-containing; Rw is the formation water resistivity.

8. The method for establishing a lithology-dependent water resistivity chart of claim 7, wherein, Further calculation is as follows: R wa = R t / F In the formula: Rwa is the apparent formation water resistivity; Rt is the deep induced resistivity. F is the formation factor.

9. The method of establishing a lithology-dependent water resistivity chart of claim 8, wherein, Further calculation is as follows: R wa = R t * Φ m / a In the formula: Rwa is the apparent formation water resistivity; Rt is the deep induced resistivity.

10. The method for establishing a lithology-dependent water resistivity chart of claim 4, wherein, In the step S3, the natural gamma ray value, the maximum value and the minimum value of the natural gamma ray of the target layer section are read, and the natural gamma ray relative value is calculated by using the formula; The calculation formula of the natural gamma ray relative value is as follows: In the formula: GR is the natural gamma ray value; △GR is the natural gamma ray relative value; GRmin is the minimum value of the natural gamma ray; GRmax is the maximum value of the natural gamma ray.

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